1. Field of the Invention
This invention relates to a circuit for controlling the tuning of an antenna. More particularly, this invention relates to a circuit for facilitating antenna operation where a plurality of antenna tuning elements are provided for optimizing impedance matching over a plurality of different frequency ranges. This invention also relates to an associated method for optimizing reception of a desired broadcasting station or channel.
2. Description of Prior Art
Conventional television antennas for receiving commercial television broadcasts are difficult to design inasmuch as such antennas must satisfy or balance among many inharmonious engineering requirements. A basic problem in attempting a set-top design that receives all VHF and UHF broadcast channels efficiently is that an antenna with an electrical extent large enough to facilitate impedance matching at each of the lowest frequency channels, particularly Channels 2 and 3, has such a large electrical extent at the highest frequency channels that the radiation patterns can exhibit sizeable frequency variations, leading to amplitude and/or phase weightings of a received broadcast signal over its frequency band and substantially diminished quality of reception.
One solution in dipole antennas sized for set-top installation is to provide individual channel matching circuits, to increase the amount of broadcast signal delivered to the receiver. For the highest numbered channels only, the problems in antenna design are less severe. Because bandwidth there is less than one percent and wavelength is less than 14 inches, antennas sized for set-top installation can exhibit inherently satisfactory impedance properties over a frequency range encompassing many channels, often the entire UHF broadcast band.
A basic problem in set-top antenna design arising front inharmonious engineering requirements is that the antenna's electrical extent is generally too little in one band and too large in another. Because of the large wavelengths and appreciable percentage bandwidths required in the lowest frequency channels (2 and 3), efficient reception in these channels, which depends on the antenna's size in wavelengths, conflicts with its height, its width and the length of its dipole arms. The superposition of an antenna configuration that can perform well at Channel 2 with one that can perform well at Channels 3 and 4, etc. and can be easily reconfigured for efficient operation at any channel is a demanding requirement.
In one recently proposed solution to the problem of TV-set-top antenna design, a television antenna device comprises a pair of electrically conductive dipole arms, a support attached to the dipole arms for supporting the dipole arms, and an electrical circuit operatively connected to each of the dipole arms and mounted to the support for tuning the dipole arms for an optimal impedance match over a plurality of different frequency ranges. A switch is operatively connected to the electrical circuit and is mounted to the support for enabling adjustment of a circuit configuration including the electrical circuit and the dipole arms to selectively tune the dipole arms for an optimal impedance match over the plurality of different frequency ranges.
The antenna device of this recent solution further comprises coupling componentry for coupling the dipole arms to a television receiver via the electrical circuit. That circuit includes a plurality of paired first and second inductors, where the first and second inductor of each pair of inductors have a common inductance and where the inductors of each pair differ in inductance from the inductors of other pairs. The switch includes means for selectively connecting the dipole arms to the coupling componentry via alternate pairs of the first and second inductors so that the first inductor of a pair is operatively connected in one circuit configuration to one of the dipole arms and the associated second inductor is operatively connected in another circuit configuration to the other of the dipole arms.
In the recently proposed antenna device, all of the first inductors are connected to a common terminal at the dipole side of the inductors and all of the second inductors are similarly connected to a common terminal, and thence to one another, on the dipole side.
It is contemplated in the afore-described recent design that the coupling componentry includes a balun transformer and a balanced two-wire transmission line connected at one end to the switch and at an opposite end to the balun transformer. In addition, an unbalanced coaxial transmission line extends from the balun transformer, while a connector is provided at one end of the unbalanced coaxial transmission line for operatively linking the unbalanced coaxial transmission line to the television receiver. In this configuration, the balun transformer is preferably a ferrite component with an impedance ratio of 1:1.